The purpose of this study is to determine the effects of race, age, gender and casual blood pressure elevation on stressor-induced opioidergic mechanisms that may contribute to the pathogenesis of essential hypertension. To test the hypothesis that deficiencies in opioid inhibition of sympathetic reactivity underlie the augmented cardiovascular activity seen in blacks and the elderly, we will use the orally administered opioid antagonist, naltrexone hydrochloride (50mg), in combination with a behavioral stressor, the foot-immersion cold pressor task, in a placebo-controlled, double-blind crossover factorial design. Cardiovascular and neuroendocrine responses within subjects will be measured at baseline, and during stress and recovery, with either placebo or naltrexone pre-treatment. Plans are to complete the final year of the grant, analyze and write up results, and present and publish findings. A no-cost extension for one year will be made in order to complete the last cell/group of subjects for this project.